webgl trendlines

Author: nicolaskruchten

Diff for: CHANGELOG.md

@@ -6,7 +6,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
-- `px.NO_COLOR` constant to override wide-form color assignment
+- `px.NO_COLOR` constant to override wide-form color assignment in Plotly Express
+- trendline traces are now of type `scattergl` when `render_mode="webgl"` in Plotly Express
 
 
 ## [4.8.2] - 2020-06-26

Diff for: packages/python/plotly/plotly/express/_core.py

@@ -843,7 +843,7 @@ def make_trace_spec(args, constructor, attrs, trace_patch):
     # Add trendline trace specifications
     if "trendline" in args and args["trendline"]:
         trace_spec = TraceSpec(
-            constructor=go.Scatter,
+            constructor=go.Scattergl if constructor == go.Scattergl else go.Scatter,
             attrs=["trendline"],
             trace_patch=dict(mode="lines"),
             marginal=None,

Diff for: packages/python/plotly/plotly/tests/test_core/test_px/test_px.py

@@ -253,3 +253,25 @@ def test_marginal_ranges():
     )
     assert fig.layout.xaxis2.range is None
     assert fig.layout.yaxis3.range is None
+
+
+def test_render_mode():
+    df = px.data.gapminder()
+    df2007 = df.query("year == 2007")
+    fig = px.scatter(df2007, x="gdpPercap", y="lifeExp", trendline="ols")
+    assert fig.data[0].type == "scatter"
+    assert fig.data[1].type == "scatter"
+    fig = px.scatter(
+        df2007, x="gdpPercap", y="lifeExp", trendline="ols", render_mode="webgl"
+    )
+    assert fig.data[0].type == "scattergl"
+    assert fig.data[1].type == "scattergl"
+    fig = px.scatter(df, x="gdpPercap", y="lifeExp", trendline="ols")
+    assert fig.data[0].type == "scattergl"
+    assert fig.data[1].type == "scattergl"
+    fig = px.scatter(df, x="gdpPercap", y="lifeExp", trendline="ols", render_mode="svg")
+    assert fig.data[0].type == "scatter"
+    assert fig.data[1].type == "scatter"
+    fig = px.density_contour(df, x="gdpPercap", y="lifeExp", trendline="ols")
+    assert fig.data[0].type == "histogram2dcontour"
+    assert fig.data[1].type == "scatter"